Fix a bug when scaling and doing offset at the same time. (At least one more remains.)

[movit] / resample_effect.cpp

diff --git a/resample_effect.cpp b/resample_effect.cpp
index 17745bc6d564e9340d756894b5f5058b34dbc1b8..2a6aecf87e8e01aebbba501a857ac73e6e61d57e 100644 (file)
--- a/resample_effect.cpp
+++ b/resample_effect.cpp
@@ -309,13 +309,13 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
        for (unsigned y = 0; y < dst_samples; ++y) {
                // Find the point around which we want to sample the source image,
                // compensating for differing pixel centers as the scale changes.
-               float center_src_y = (y + subpixel_offset + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
+               float center_src_y = (y + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
                int base_src_y = lrintf(center_src_y);
 
                // Now sample <int_radius> pixels on each side around that point.
                for (int i = 0; i < src_samples; ++i) {
                        int src_y = base_src_y + i - int_radius;
-                       float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y), LANCZOS_RADIUS);
+                       float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y - subpixel_offset), LANCZOS_RADIUS);
                        weights[(y * src_samples + i) * 2 + 0] = weight * radius_scaling_factor;
                        weights[(y * src_samples + i) * 2 + 1] = (src_y + 0.5) / float(src_size);
                }